Sound recording system



R). M.v oTls 2,082,906?

sUND RECORDING SYSTEM f 1 Jung 8, 1937.

original Filed July 17, 1929 z sngetsfsqget' 1 y j Arrokwex June s, 1937. R M, ms 2,082,900

SOUND RECORDING SYSTEM VOlriginal Filed July 17, 1929 2. Sheets-Sheet 2 xi. ma Wm Ik@ f/V VEN TOR /?u.sse// M Offs) 5y Arrow/5x Patented June f8, 1937 UNH'EE STATES smear ce SOUND RECORDING SYSTEM Russell M. Otis, Alhambra, Calif.

19 Claims.

My invention relates to a novel system for indicating or recording various phenomena, and more particularly to a novel apparatus for recording sounds or other phenomena on a motionpicture film or other photo-sensitive element, the

present application being a division of my copending application entitled Process of and apparatus for photographically recording sounds, iiled July 17, 1929, Serial No. 378,994.

As disclosed in that application, it is known that an exposure of a photosensitive element can be obtained by positioning electrodes on opposite sides thereof and impressing a momentary high potential across these electrodes. The re- 15 sulting exposure, when subjected to the usual developing methods, appears in the form of a large number of lines extending radially from the area oi contact between the electrode and the photo-sensitive element. Such ligures are known in the art as Lichtenberg igures.

As further set forth in my co-pending application, I have found that it is possible to form an exposure in the area between the electrodes if the voltage gradient is sufficiently high, and 25 by conning the discharge it is possible to expose a portion of the photo-sensitive element in the form of a minute line which is preferably equal to or less than l/llo@ of an inch in width, and

ol a length equal to or less than the space on the motion-picture film allotted to a sound track. By suitably modulating the potential impressed across the electrodes as a function of the sound or other phenomena to be recorded, and by moving the photo-sensitive element between these 35 electrodes, I have found it possible to accurately record the phenomena on the film, the developed iilm showing a plurality oi lines extending across the sound track, each line being of equal intensity across this sound track, but succeeding 40 lines varying in density with respect to each other. The result is a sound track which appears quite similar to those sound tracks at present known in the art as the variable density type.

The present invention is directed to a system of recording by the use of a modified form of this type of discharge, the resulting sound record containing aplurality of lines, each successive line being oi different density, and each line itself having a density which varies across the 50 sound track. Such a record is a combination of the so-called variable density and variable area records at present Well known in the motion-picture art. This type of record is very desirable, and gives a very accurate reproduc- 55 tion when used in conventional reproducing systems or in systems especially designed therefor.

It isv an important object of the present invention to provide a photo-sensitive element, such as a motion-picture film, which includes an area or track containing a plurality of such lines, successive lines being of different density, and each line being of varying density throughout its length.

A further object of the invention lies in the provision of anovel apparatus for forming such a sound track, and my experimentshave shown that several methods of obtaining such arecord are possible. In one of these methods, one or both of the electrodes are formed of a high-resistance material such as silicon, and the current is conducted therethrough in a path which ex'- tends substantially parallel to the surface ofthe light-,sensitive element; A voltage drop is thus set up, so that the voltage between the electrodes at any point is :equal to the applied voltage across the electrodes less the Voltage drop in the electrodes taking place in that portion of the electrode lying to one side of the section under consideration. The discharge thus set up between the electrodes is of non-uniform intensity and the resulting exposure is a function of the intensity of this discharge.

It is an object of this invention to provide a method and apparatus of recording wherein at least one of the electrodes is formed of a material having a relatively high resistance, whereby the current flowing therethrough sets up a voltage drop, the magnitude of this drop depending upon the distance the current has travelled.

Another system whereby sucha desirable sound record may be formed includes the formation of electrodes in such a manner that the gap formed therebetween is tapered. The photo-sensitive element is positioned in this gap, and due to the taper thereof the gradient set up therein will be non-uniform throughout the length of the gap, and the discharge will be much more intense in the, narrower portion of the gap than in the wider portion thereof.

It is van object of this invention toprovide a recording system wherein a relatively long and narrow discharge is set up, this discharge being of non-uniform intensity throughout its length.

A further object of the invention is to provide such a non-uniform discharge, and to modulate this discharge with the phenomena to be recorded.

A further object of the invention is to provide such a tapered gap between a pair of electrodes so arranged that that portion of the tapered gap not occupied by the photo-sensitive element is substantially lled with a suitable dielectric.

My invention also includes the combined use of a high-resistance electrode structure and a structure. It is an object of this invention to provide a recording system combining a hi"gh'-resistanceH electrode with a tapered gap in which the photo- A.

sensitive element is positioned.A

Other systems whereby such a desirable" sound record may be produced will be apparent from" the disclosure hereinafter.

' Y Further objects of the invention lie in a novel electrode structure wherein fringing of the discharge is prevented,A and whereinv the resultant exposure may be limited in shape to a desired area.

Otherobjects and advantagesof the invention will'v be made evident hereinafter. YReferring to the drawings, in which I have new type of sound record,- Y

Fig. 1 illustrates one type of high-resistance electrode structure in combination with a typical'modulating circuit.

Figs. 2 and 3 illustrate other types of highresistance electrode structures, Fig. 2 being taken along the line 2--2 of Fig. 1. f

vFigs. 4 Vto '7 illustrate varying-gap electrode structures.

Figs 8 and 9 illustrate combinations of the Varying-gap and high-resistance electrode structures. Fig. 10 diagrammatically illustrates a Sound track, greatly magnified, made by the electrodes of my invention.

The general appearance of the invention may be best understood by reference to Fig. l, which illustrates one form of the electrode structure in combination with one type of modulator circuit more particularly set forth in my co-pending application supra. The particular circuit shown in Fig. 1 is not a part of this invention, and it should be clearly understood that numerous other modulating circuits well known in the art might be used. Essentially, however, the circuit shown in Fig. 1 comprises an oscillator tube l5 which sets up a high-frequency oscillation which is modulated by a modulator tube I6 in response to the variations in the phenomena to be recorded. When used for recording sound, a microphone Il is coupled with the modulator tube i6 in such a manner that the high-frequency oscillations are modulated bythe sounds picked up by this microphone in any well-known manner. This modulated potential 'is impressed across .a pair of electrodes, this being accomplished in the circuits shown in Fig. 1 including an auto-transformer 2!! having output conductors 2l and 22, the entire modulating system being hereinafter termed a current supply means 25.

Two electrode structures are illustrated in Fig. 1, termed respectively primary and secondary electrode structures 27 and 28. vThese structures are spaced a distance apart substantially equal to the thickness of a photo-sensitive element on VVwhich a record is to be impressed, this photo-sensitive element being illustrated and shown several possible systemsv producing my Y high electrical resistance.

hereinafter referred toas comprising a motionpicture film 29 having a Celluloid backing 30 and an emulsion surface 3i thereon, and being provided with sprocket holes 32 in the usual manner. That portion of the motion-picture lm lying between the lines A-A and B-B comprises the sound track 33 on which the recording takes place, the pictorial image being recorded to the left of the sound track as viewed in Fig. 1.

In this form of the invention the primary electrode structure 2l comprises a pair of blocks V35 and Sii which support a blade or knife-edge electrode 38.*' lIn practice I prefer to form the blocks 35 and of an insulating material and to utilize for the electrode "o either an ex- .tremely thin foil of a relatively high-resistance material or some other thin layer or deposit of such a material. This high-resistance material,

however, has a much higher conductivity than the blocks 35 and 355. These blocks thus support Vthe electrode S8, and the whole electrode struc- The thickness of the electrode 38 is preferably less than V1000 of an inch, this being necessary in order to accurately record on a conventional m0- tion-picture iilm moving at the usual speed all of the overtones in the sound to be recorded. In my co-pending application the material forming this electrode is a metal having a very high conductivity, but in the instant application it is desirable to use a material having a relatively Such a material is silicon, which may, by carefully Working, and in some cases by a special process, be formed into a foil less than 1/1000 of an inch in thickness. Certain metals also have a high enoughresistance to be successfully used in forming the electrode 38, and certain stones or minerals having a high resistance can be used, where these are easily polished and especially in the forms to be later described. So also certain alloys are useful in this capacity, and it is entirely possible to form a very thin coating on one or both of the blocks ,by spraying thereon such high-resistance materials in molten or molecular state, thereby building up a coating of the required thickness. It is also possible to apply such a coating by other means, and a satisfactory electrode can be obtainedV by mixing a powdered conducting material such as lampblack with certain other materials such as, for instance, sodium silicate. Certain other compounds formed of carbon and bakelite vcan also be used in some instances. The particular material utilized depends upon a number of factors, including the Workability and the desired resistance. In certain instances it isV desirable to use the mixtures or alloys, for. obviously it is possible to secure an electrode of any desired resistance, though in other instances it is equally effective to utilize certain of the other materials and design the current supply means so that the desired effect is obtained. Certain other factors which must be taken into account when determining the resistance or setting of the current supply means will be more clearly set forth hereinafter.

The secondary electrode structure 28 is similarly constructed, utilizing blocks 42 and 43 as a supporting structure for an electrode 44. In the form shown in Figs. l and 2, the electrode 44 lies in the same plane as the electrode 38, and the thickness thereof preferably does not exceed 1/1000 of an inch. In this `form of the invention, the electrode Mi may be either an electrode formed of a high-resistance material, such as outlined above, or an electrode formed of a material having a high electrical conductivity. `Both the eleccurs across that portion thereof which is in close proximity to the photo-sensitive element 29. It is thus preferable that the current pass through this high-resistance electrode in a direction sub stantially parallel to the surface of the photo-l sensitive element, 'and thus I have illustrated `termina'l portions t8 and 39 on the electrode 38 between which terminal portions the current iiows, the former terminal portion being connected to the conductor 2l. The conductor portion t9 is connected to a conductor 50 which is in turn connected to a terminal portion 45| of the electrode M, there being another terminal portion 52 connected to the conductor 22.

Considering, for instance, that the electrode 38 is of high-resistance material, and the electrode M is formed ofA a material having arrelatively high conductivity such, for instance, as platinum, it will be apparent that the potential between the electrodes at the vsection A-A will be substantially equal to the potential ofthe current supply means at anyl instant. However, the potential between the electrodes at the section C-C will be niuchless due to the voltage drop taking place in the electrode 33 when the current iiows between the terminal portions t8 and 49. In fact, the voltage between the electrodes at the section VC---C will be substantially equal to the voltage of the current supply means at any instant, less the voltage drop set up by the current in passing through that portion of the electrode 38 to the left of the section C-C. This voltage drop is proportional to the product of the current and the resistance of that portion to the left of the section C-C. It will thus be apparent that the voltage' between the electrodes at the section A-A is much greater than between these electrodes at rthe section C-C, and that both of these voltages are higher than the voltage between the electrodes at the section B-B.

It is thus apparent that the discharge set up between the electrodes will be non-uniform between the sections A-A ar1dYB--B; in other words, this discharge will progressively decrease from one boundary of the sound track to the other. By so controlling the current supply means with respect to the resistance of the electrede 38 that the voltage between the sections A.-A is suicient to expose the film, while the voltage at the section B-B is insufficient to expose the film, or at least exposes this iilm to a lesser degree at the` latter section, the result is that a line will be formed on the photo-sensitive element 29 which willbe apparentafter development, this line being much more dense adjacent that boundary of the sound track indicated by the section A-A than at any other section along the length of this line. In fact, the exposure will gradually fade 01T. Such a line would appear similar tothe line 53 of Fig. 10, the boundaries of the sound track being represented by the lines A-A and B-B.v Necessarily, Fig. l0 is diagrammatic inasmuch as it is impossible to exactly represent the fading orf. This figure viewed at a distance does, however, give the general impression of the fading which takes place.

If, now, the potential between the conductors El and 22 is modulated, for instance, by the Sounds to be recorded, the result is that the discharge at a given section is correspondingly made greater o1' smaller. Thus, if the lm 29 is moved relative to the electrode structures, the result is a series ci lines indicated in Fig. 10, each successive line being of different density than the adjacent lines. The term line is not entirely correct, especially when referring to Fig. 10 wherein the length of the sound track has been greatly distorted so that the fading can be represented. In reality, the spaces between the lines of Fig. l0 do not appear completely unexposed to the extent represented, as will be apparent to those skilled in the art.

If the electrode ifi is also made of high-resistance material, a voltage drop will also take place therein in the same manner as the voltage drop which takes place in the electrode 33.

In any event the blocks positioned adjacent `the knife-edge electrode prevent a spreading of the discharge along the surface of the photosensitive element. Such a discharge would inevitably take place if some means were not utilized for preventing it, and the resultirrg exposure It should 4not be understood, however, that I L am limited to two knife-edge electrodes. Thus, in Fig. 3 I have illustrated a knife-edge electrode 5i above the film, and have illustrated a relatively massive electrode 58 below this ilm, this latter electro-de being in the form of a plate or i bar, `for instance. Such a system is especially advantageous when the emulsion side of the iilm moves in contact with the knife-edge, and it has been found that the spreading effect whenlutilizing a relatively massive electrode such as the c' electrode 58 is not materially greater than when using a knife-edge electrode such as the electrode ist. In the system shown in Fig. 3, the conductor 5B is shown as being connected to a terminal portion 59 of the electrode 58, the conductor 22.' being connected to a terminal portion G thereof. In this forni of the invention either the electrode 5l or the electrode 58, or both, may be formed of high-resistance material, and the result will be similar to the results previously described. If the electrode 58 is formed of a highresistance material, such as` silicon or suitably polished stones, it is sometimes desirable to utilize separate low-resistance electrodes for sending current through the high-resistance electrode 58.

This may be accomplished by utilizing a plate electrodeon opposite ends of the electrode E8, these plate electrodes being in pressure contact therewith.l

As described in my co-pending application, it

is also: possible to substitute a roller for the `electrode 53, or a roller incorporatedin a sprocket. Regardless ofthe electrode utilized, it is possible to form thisof material having a relatively high resistance so that the desirable effect is obtained. A second system whereby the desirable type of record shown in Fig. 10 may be obtained is to use two electrodes so disposed as toiorm a tapering gap therebetween and in which the lm is positioned. Thus, in Fig. 4 I have illustrated blocks il@ and 8l forming a supporting structure for a primary knife-edge electrode 82. The lower edge of this electrode is not, however, in surface contact with the photo-sensitive element 29 over the total width of the lsound track represented between Vthe lines A-A and B-B. Instead, however, substantial contact between the electrode and the photo-sensitive element takes place at the section B-B, while a gap exists between the electrode and the'surface of the photo-sensitive elementl at Vthe section A-A. A secondary electrode Eil is positioned below the photo-sensitive element and in surface contact therewith, this secondary electrode being in the form of a bar or plate. In this embodiment of the invention both the electrodes 82 and 84 are formed of a metal having a high electrical conductivity, one of these electrodes being connected to the conductor 2l and the other to the conductor 22 or" the current supply means 25.

There is thus set up between the electrodes 82 and Sli a discharge of non-uniform intensity, this Vdischarge being more intense at the section B--B than at the section A-A due to the diiierence in spacing between the electrodes. The result is that the discharge exposes the lm to a greater degree at the section BB than at the section A-A, thus forming a line of Variable density on the photo-sensitive element. By modulating the potential and moving the film therebetween,

the result is a series of exposures along the sound track, each exposure varying in lntensity across the sound track and succeeding exposures varying in intensity along the sound track.

In Fig. 5 I have shown a system utilizing two electrode structures having knife-edge electrodes, one ofA these electrodes being designated a primary electrode 88 and providing an angled surface 89 and the other of these electrodes being designated a secondary electrode 90 and providing a contact-ing surface 9i. Y

Similarly, in Fig. 6 I have shown a pair of electrode structures in which both electrodes are in the form of knife-edges, each being provided with an angled surface whereby the distance between the electrodes increases even greater per unit of distance across the sound track.

Fig. 7, however, shows the system most easily constructed, one electrode structure being formed with a knife-edged primary electrode i90, which is in surface contact with the film across the sound track, a secondary electrode being indicated by the numeral il and being in the form of a tapered block or rod having an angled surface EQ2 spaced varying distances from the surface of the lm so as to cooperate with the electrode iii@ in providing a varying gap across the sound track. In this form of the invention, that portion of the gap which is not required for the movement of the film is filled with a dielectric indicated by the numeral |03, so that the iilm moves in contact with this dielectric and is thereby held in correct relationship relative to the electrode ll. In-some instances it is advisable electrode l HI of high-resistance material in combination with a block electrode lll having an angled surface il 2. As shown in Fig. 8, the conductor 2l is connected to that portion of the electrode Il@ which lies the closest to the electrode l l l.

The effect of the high-resistance electrode is thus additive relative to the eiect of the tapering gap, for not only is the voltage of the section B-B lower than at the section A-A due to the voltage drop across the electrode H 0, but the voltage gradient is also lower because of the added spacing between the electrodes at the section B-B. Nor is it necessary to use an angled electrode of low resistance and a knife-edge electrode of high-resistance material, `for both may be of high-resistance material or the angled electrode may be alone of high-resistance material with the knife-edgeelectrode of low-resistance material.

It is sometimes desired to connect these electrodesfin subtractive relation, in which case the electrodes may be connected, as shown in Fig. 9, the upper electrode I l0 being the high resistance electrode, and the electrode I Il being the lowresistance electrode. The voltage across the electrodes at the section A-A will be equal to the instantaneous voltage of the current supply means 25, but the discharge therebeyond will be lessened due to the added spacing of these elecl trodes at this section. This spacing ofV the electrodes is much smaller at the section B-B, thus tending to increase the discharge thereat. On the other hand, thev voltage between the electrodes at the section B-B is less than at the section A-A considering the voltage drop in the electrode HB. Whichever eect is the greater will control the varying density of the resulting image.

While I have shown the angled surfaces of the electrodes as being disposed in a straight line, it should be understood that this is not necessary to the invention. These angled surfaces may be formed on a suitable curve whereby the voltage gradient between the electrodes at any section of the sound track is dependent on this curve. This is especially desirable inasmuch as it allows compensation for other errors which might occur in this system due to the use of a particular apparatus. So also, the curve of this angled surface may be designed in conjunction with the shape of the H and D curve representing the relationship between densityrand exposure with a given developer and a particular lm utilized. Thus, ifthe operator is working on a curved por-` tion of the I-I and D curve distortion might be introduced into the sound record due to this curve, but if the shape of the angled surface was so designed with relation to the particular portion of this I-I and D curve utilized, this distortion can be compensated for.

It should thus be apparent that I am not limited to a tapering gap in which the distance between the electrodes increases uniformly across the sound track. Furthermore, while I have shown` the knife-edge electrode as extending perpendicularly across the sound track, this is not essential to the invention, it only being necessary that this electrode extend transversely whether or not such transverse extensionr is perpendicular. Finally, my system is novel in other capacities than in the recording of sound on -a motionpicture lm, and can be used with various other photo-sensitive elements whether these are moving or stationary relative to the `electrode structures. i

I claim as my invention: y

1. In a recording system for recording on a photo-sensitive element, the combination of: a primary electrode positioned close to said photosensitive element and formed of a high-resistance material; a current source for sending a current through said primary electrode in a direction across said photo-sensitive element whereby a voltage drop takes place across said primaryr electrode; and a secondary electrode means positioned on the opposite side of `said photosensitive element from said electrode and electrically connected to said current source, said current source developing suflcient potential to expose said photo-sensitive element.

2. A combination as dened in claim l in which said primary electrode provides a pair of terminal means on opposite ends thereof, one of said terminal means being connected to one terminal of said current source, the other terminal oi said current source being connected to said secondary electrode means, and including a conducting means connecting said secondary electrode means and the remaining terminal means of said primary electrode.

3. In a recording system for recording phenomena on a moving photo-sensitive element the combination of: primary and secondary electrodes positioned on opposite sides of said moving photo-sensitive element, at least one of said electrodes being in the form of a knife-edge eX- tending transversely relative to the direction of movement of said photo-sensitive element, said primary electrode being formed of high-resistance material and providing a pair of terminal means spaced from each other in the direction of the length of said knife-edge; means for impressing a high potential across said electrodes and varying in response to the variations of the phenomena to be recorded, said means including a conductor connected to one terminal means of said primary electrode, and another conductor connected to said secondary electrode; and a conducting means connecting said secondary electrode and the other terminal means of said primary electrode whereby the voltage gradient between electrodes is non-uniform along said knifeedge electrode at any instant.

4. In a system for recording on a photo-sensitive element, the combination of primary and secondary electrodes positioned on opposite sides of said photo-sensitive element and spaced from each other to form a tapering gap; means for establishing a potential diiference between said electrodes of suicient magnitude to expose that portion of said photo-sensitive element lying therebetween, but of insufcient magnitude to puncture said photo-sensitive element; and means for confining said discharge to prevent spreading thereof.

5. A combination as defined in claim 4 including a dielectric medium filling that portion of said tapering gap not occupied by said photo-sensitive element.

6. A combination as defined in claim 4 in which at least one of said electrodes is in the form of a knife-edge, and in which said means for coniining said discharge comprises means adjacent said knife-edge and contacted by said photo-sensitive element.

. 7. A combination as defined in claim 4 in which one of said electrodes contacts said photo-sensitiveelement throughout the length of this electrode, the other ofsaid electrodes being spaced unequal distances from said light-sensitive element to iormsaid tapering gap. v 8. In a system for recording on a photo-sensitive element, the combination of a primary electrode in the form of a thin element providing an edge in surface contact with said photo-sensitive element throughout the length of said electrode; a secondary electrode on the opposite side of said photo-sensitive element from said primary electrode and providing an inclined surface spaced varying distances from said photo-sensitive element and oppositely disposed relative to said edge of said primary electrode; and means for impressing a` potential across said electrodes sufficient to expose that portion of said photosensitive element lying therebetween, but of insufficient magnitude to puncture said photosensitive element.

9. In a system for recording on a photo-sensitive element, the combination of: an electrode on one side of said photo-sensitive element; an angled electrode on the other side of said photosensitivey element and spaced from said rstmentioned electrode to form a tapering gap at leastone of said electrodes being formed of a material having a relatively high electrical resistance; Vand current supply means impressing a potential difference between said electrodes whereby current iiows through said electrode of high-resistance material in a direction across said photo-sensitive element.

l0. An electrode structure comprising:` an electrical conductor providing a discharge edge; and a tapered solid dielectric member adjacent said discharge edge and providing a contacting surface extending at an angle to said discharge edge, whereby said discharge edge is closer to said contacting surface at one end than at another end.

11. An electrode structure comprising: a member formed of high-resistance material providing a discharge edge; and two'terminal means on said member and spaced from each other in the direction of said discharge edge whereby a current flowing therebetween moves substantially in the direction of said discharge edge and sets up a voltage drop therealong.

12. An electrode structure comprising: a member formed of silicon and providing a discharge edge; and two terminal means on said member and spaced from each other in the direction of said discharge edge whereby a current iiowing therebetween moves substantially in the direction of said discharge edge and sets up a voltage drop therealong.

13. An electrode structure comprising: a pair of electrodes spaced from each other to dei-lne a gap in which a discharge may be established, one of said electrodes being formed of a relatively' high-resistance material; means for forcing an electric current through said one of said electrodes which is formed of high-resistance material and in a direction along said other of said electrodes whereby a voltage drop takes place in said highresistance electrode to decrease the potential existing between said electrodes along said gap, thereby setting up an electric discharge of nonuniform intensity in said gap.

14. In combination in a system for recording on a photo-sensitive element: means for establishing a long and narrow discharge through said photo-sensitive element which discharge is of much greater intensity at one portion of its length than at another portion of its length and is of intermediate intensity between said portions, said means including a knife-edge electrode on one side of said photo-sensitive element, an auxiliary electrode meansV on the opposite side of said photo-sensitive element, and a means for establishing a potential diierence between said electrodes to establish a discharge sufficient to expose said photo-sensitive element.

15. A combination as dened in claim 14 including means for conining said discharge to an area not substantially wider than said'knife-edge.

16. In a recording system for recording phenomena on a moving photo-sensitive element, the combination of means including electrodes on opposite sides of said moving photo-sensitive element for setting up a lineal discharge between said Velectrodes and of non-uniform intensity in the direction of its length, the intensity gradually varying from one portion of said lineal discharge to another portion thereof; and means for varying the intensity in all portions of said lineal discharge in response to the variations of Vthe phenomena to be recorded whereby a Varying intensity discharge is set up between said electrodes suflicient toxpose said photo-sensitive element therebetween but insufcient to puncture said photo-sensitive element.

1'7. In combination with a photo-sensitive element: a primary electrode formed of a high resistance material and providing a discharge edge positioned adjacent said photo-sensitive element; means including a current source for sending` current through said primary electrode in a direction along said discharge edge Ywhereby a voltage drop takes place along said discharge edge; and a secondary electrode connected to said current source and cooperating with said discharge edge of said primary electrode in bounding a discharge space in which said current source sets up a` discharge which exposes said photo-sensitive element, said discharge being of non-uniform intensity along the length thereof due to the voltage drop along said d ischarge edge.

18. A method of recording on a photo-sensitive element, which method includes the steps of: establishing a long and narrow discharge through said photo-sensitive element and of much greater intensity at one portion ofV its length than at another portion of its length and of intermediate intensity between these portions, said discharge at said one portion of the length of said discharge being sucient to expose said photosensitive element, and said discharge of said other portion of said discharge being of insulcient intensity to materially expose said photosensitive element, said intermediate intensity between said portions exposing said photo-sensitive element in decreasing amounts from said one portion toward said other portion.

19. A method as defined in claim 18 including the additional steps of moving said photosensitive element transversely with respect to said discharge; and varying the intensity throughout the lengthof said discharge in response to the variations in the phenomena to be recorded whereby successive portions of said photo-sensitive element are exposed over varying fractions of the length of said discharge.

RUSSELL M. O'IIS. 

